bug#34884: guix describe fails with --format=json and --format=recutils

[Ludovic Courtès]

Hi Oleg,

Oleg Pykhalov <address@hidden> skribis:

> JSON format:
>
> address@hidden ~/src/guix$ ./pre-inst-env env 
> GUIX_PACKAGE_PATH=$HOME/src/guix-wigust:/tmp/noexist:/tmp/noexist:/tmp/noexist:/tmp/noexist:/tmp/noexist:/tmp/noexist:/tmp/noexist:/tmp/noexist:/tmp/noexist:/tmp/noexist:/tmp/noexist:/tmp/noexist:/tmp/noexist:/tmp/noexist:/tmp/noexist:/tmp/noexist:/tmp/noexist:/tmp/noexist
>  guix describe -p ~/.config/guix/current --format=json
> [{"name":"guix","url":"https://gitlab.wugi.info/guix/guix.git","commit":"4161deb4549c39b7d4801cc8aa63c365d19fc649"},{"name":"guix-wigust","url":"https://gitlab.wugi.info/guix/guix-wigust.git","commit":"f6dfa5fc08824ebe5bdc42ea35ff0e040245c8c0"}]
> {"name":"GUIX_PACKAGE_PATH","paths":["/home/oleg/src/guix-wigust","/tmp/noexist","/tmp/noexist","/tmp/noexist","/tmp/noexist","/tmp/noexist","/tmp/noexist","/tmp/noexist","/tmp/noexist","/tmp/noexist","/tmp/noexist","/tmp/noexist","/tmp/noexist","/tmp/noexist","/tmp/noexist","/tmp/noexist","/tmp/noexist","/tmp/noexist","/tmp/noexist"]}

Initially the intent was to warn users that ‘GUIX_PACKAGE_PATH’ is set
and not captured in the output of ‘guix describe’, because fundamentally
it cannot be captured reliably.

Thus, what about something as attached instead?

Thanks,
Ludo’.

diff --git a/guix/scripts/describe.scm b/guix/scripts/describe.scm
index 7d0ecb0a4d..b6287d3a4c 100644
--- a/guix/scripts/describe.scm
+++ b/guix/scripts/describe.scm
@@ -1,5 +1,5 @@
 ;;; GNU Guix --- Functional package management for GNU
-;;; Copyright © 2018 Ludovic Courtès <address@hidden>
+;;; Copyright © 2018, 2019 Ludovic Courtès <address@hidden>
 ;;; Copyright © 2018 Oleg Pykhalov <address@hidden>
 ;;;
 ;;; This file is part of GNU Guix.
@@ -85,7 +85,9 @@ Display information about the channels currently in use.\n"))
         (format #t "~%GUIX_PACKAGE_PATH=\"~a\"~%" string))
        ('channels
         (format #t (G_ "~%;; warning: GUIX_PACKAGE_PATH=\"~a\"~%")
-                string))))))
+                string))
+       (_
+        (warning (G_ "'GUIX_PACKAGE_PATH' is set but it is not 
captured~%")))))))
 
 (define (channel->sexp channel)
   `(channel